Method for measuring the geometry of an object by means of a co-ordination measuring device

ABSTRACT

The invention relates to a method for measuring the geometry of an object ( 12 ), particularly a work piece or a tool, by means of a co-ordination measuring device ( 10 ). The geometry of an object ( 12 ) is recorded by an optical sensor ( 14 ), for example a camera, and is represented in the form of an image content ( 32 ). Geometric structures ( 60 70 ) in the image content adapted to the measurement of the object ( 12 ), such as geometric elements or contours, are selected and subsequently evaluated. The aim of the invention is to enable even non-experienced operators to carry out a measurement in a fast and fault-free manner. When the image content ( 32 ) is changed, it is automatically analysed in relation to the geometric structures ( 60 - 70 ) adapted to the object measurement ( 12 ), and the adapted structures are marked and prepared for subsequent evaluation.

[0001] The invention concerns a process for the measurement of an objectgeometry, especially a workpiece or tool geometry, by means of acoordinate measuring device, whereby the object geometry is recorded bymeans of an optical sensor, such as a camera, and represented as animage content, and whereby, within the image content, geometricstructures suitable for the measurement of the object, such as geometricelements or contours, are selected and subsequently evaluated.

[0002] To date, coordinate measuring devices with image processing haverequired the triggering of all, or of the significant, image processingfunctions by manual interaction. Thus, for example, the image is savedmanually after the coordinate measuring device has been set to theoptimum lighting state and the correct position. After the image contentis manually saved, a similar manual selection of the geometricstructures suitable for measurement of the object takes place, bysetting windows that select the area of interest. In this process, itmust be taken into account that the selection is generally performed onthe basis of the user's subjective impression, making measurement orprogramming into a time-consuming process, which also frequentlyinvolves intrinsic errors.

[0003] The present invention is founded on the problem of developing aprocess for the measurement of an object geometry, of the type describedabove, in such a way that the measurement operation can be performedquickly and without errors, even by untrained operators.

[0004] In order to solve this problem, it is proposed, inter alia, that,at the time of any modification of the image content, the image contentis automatically searched for the geometric structures suitable for themeasurement of the object, and the suitable structures are marked andmade available for further evaluation. This process, relative to priorart, achieves the advantage of eliminating the need for time-consumingselection by an operator of geometric structures suitable for themeasurement. The automatic search for geometric structures is performedat the time of any modification of the image content of the opticalsensor, so that, in the represented image content, the geometricstructures suitable for the measurement are marked and updated on aconstant basis. The process especially provides for modification of theimage content to take place when modification of the opticalmagnification and/or of the position of mechanical axes of thecoordinate measuring device and/or of the light intensity takes place.In this way, the process achieves the additional advantage that auser—for example, at the time of modification of image processingfunctions—always obtains an updated image content with marked geometricstructures for measurement of the object geometry. Preferably, themodification of the image content will be represented by a signal.

[0005] The process especially provides for the signal representing themodification of the image content to be produced by a control unit of azoom lens of the coordinate measuring device at the time of modificationof the optical magnification. It also provides for the signalrepresenting the modification of the image content to be produced by areplacement unit, such as a revolving holder, when the modification ofthe optical magnification is produced by replacement of the objective.

[0006] A further development provides for the signal representing themodification of the image content to be produced by an actuationcontrol, such as CNC control, when the state of a counter on at leastone axis of the coordinate measuring device remains constant for longerthan a predetermined interval of “dead time”, following a positionchange, It also provides for the signal representing the modification ofthe image content to be produced by a lighting control, when a nominallighting value, following a modification of lighting, remains within atolerance range for longer than a predetermined interval of “dead time”.Moreover, an additional optical sensor can supply the signalrepresenting the modification of the image content when the constancy ofthe light ratios gives rise to an inference with regard to themodification of the image content. This is especially the case when theobject geometry shows a lattice structure and, upon modification of itsposition, the modification of the light ratios is constant withinitself.

[0007] In addition, it is possible for the signal representing themodification of the image content to be alternatively produced by anoperator, preferably by pressing a button. This is particularlyadvantageous when the operator, for example, desires to update the imagecontent, without performing the aforementioned modifications with regardto optical magnification, position of the mechanical axes or lightratios.

[0008] In order to give an operator the option of performingpredetermined measurements of the object geometry, it is advantageous toprovide the option for the operator to manually select the markedgeometric structures—for example, through the control of a monitor bymeans of an input device such as a mouse, touchpad, touch screen and soforth.

[0009] Moreover, it is possible that the geometric structures which areautomatically marked according to the invention can be automaticallyincorporated into a characteristic list at the time of a newmodification of the image content. This is especially significant forthe programming of test programs. In addition, it is possible andadvantageous that the automatically preselected elements can be manuallydeleted and modified by the operator, whereby, especially, an area ofinterest from the represented object geometry—such as a contour—can bedefined by the operator him/herself.

[0010] In an especially advantageous procedure, the image content isautomatically searched for regular geometric elements, such as straightlines and/or circles. The automatic search for regular geometricelements, such as straight lines and/or circles, has the advantage thatthey can be relatively easily and quickly selected from the recordedimage content and marked, whereby these regular geometric elements arealso especially suitable for the subsequent measurement of the objectgeometry—that is, for further evaluation.

[0011] An additional feature of the process, which is itself of aninventive nature, provides that, for identification of the relevantgeometric structures suitable for the measurement of the object, acomparison of the recorded geometric structures of the object geometrywith at least one regular geometric element, such as a circle and/or astraight line, is performed, and that the geometric structures of theobject geometry which show the least deviation in shape, relative to theregular geometric element, are marked.

[0012] An additional inventive process provides for the marking of thegeometric structure suitable for measurement of the object to take placein such a way that an area of interest is automatically adjusted,preferably through the use of optimization, to the marked/detectedgeometric structure, such as a geometric element or a contour.Preferably, the optimized adjustment is performed by means of apredetermined part tolerance. The process also provides for theautomatic adjustment to be performed with reference to the direction andproportion of the marked geometric structure. By reduction in an imageprocessing window, a more precise evaluation for the purpose ofmeasuring the object geometry can take place. With regard to automaticadjustment with reference to part tolerance, it should be noted that theindividual setting, for example, of a measurement program can take placewhen processing a plurality of identical object geometries, whereby thegeometric structures to be examined within the object geometry—that is,the workpiece—can possibly be subject to tolerance fluctuations, makingit preferable, if at all possible, to exclude intervention by anoperator.

[0013] An additional feature of the process, which is itself of aninventive nature, provides that, out of the quantity of preselectedgeometric structures, the structure located closest to the middle of arepresented image section is automatically selected. The advantageinherent to this process feature lies in the fact that, when an operatoris measuring object geometries with a plurality of identical geometricstructures—such as, for example, a semiconductor chip with etchedtransistor structures—no post-processing of the marked geometricstructures must take place, because, according to the invention, thegeometric structure located closest to the middle of an image section isautomatically selected and is accordingly made available for furtherevaluation, i.e. for measurement.

[0014] A further inventive process for the measurement of an objectgeometry provides that, as a function of the object classes to bemeasured and/or the mode of operation of the coordinate measuringdevice, strategies for the marking of the geometric structures suitablefor the measurement of the object are selected and/or determined. Objectclasses, for example, may depend on the material of the object to bemeasured, which may consist of metal, plastic or other materials.Moreover, the surface of the object to be measured may show a variety ofproperties with regard to reflection and color, so that, accordingly,the recording of the object geometry by means of the optical sensor mayshow a variety of different qualities. In addition, the mode ofoperation of the coordinate measuring device—such as, for example,direct light mode or transmitted light mode—may have an effect on therepresentation of the object geometry. Strategies for the search of theimage content in order to locate geometric structures suitable for themeasurement of the object may include, for example, various imagefilters and/or contour filters, such as dilation, erosion or Sobelfilters. In this context, an image content—for example, in the form of ahistogram—is searched for contour transitions according to a variety ofalgorithms.

[0015] Especially proposed is a process itself of an inventive naturewhereby, in the course of an automatic sweep of several objects of thesame type, both an image processing algorithm and the image processingwindow are allocated to an average value of the respective geometricstructures. In this way as well, the measurement of an object geometryis speeded up and intervention by an operator is avoided.

[0016] A further development of the process according to the invention,which is similarly based on an inventive idea, provides that, as afunction of the geometric structures suitable for the measurement of theobject, various processes such as scanning or point-by-point measurementare accessed for the purpose of evaluation of a shape, such as a circle,a straight line or similar, or for the purpose of evaluation of adimension, such as diameter, distance, angle or similar. For example,total image scanning or individual image scanning processes may be usedas measurement processes for the evaluation of a shape and/or adimension. For the measurement of dimensions, point-by-point measurementis especially suitable. In order to simplify the selection of thegeometric structures, such as contours and/or geometric elements,available nominal files are used for comparison. Stored in the nominalfiles are nominal structures or nominal geometries; during the search ofthe image content, these are compared with actual geometries, wherebythe principle of the least deviation in shape is preferably used forcomparison.

[0017] Finally, the process according to the invention is distinguishedby an additional feature, which is itself of an inventive nature,whereby an image processing contour, taken from the image content, isprovided, within a pixel raster, with additional information with regardto subpixel coordinates within the pixel. In this way, it is possible toincrease the position of the measurement process, because the pixelrasters often show structures that are larger than the structures to bemeasured. In this connection, the contours can be described by means ofFreeman chains, whereby appropriate subpixel bytes are added to eachbyte of the Freeman chain.

[0018] When image processing operators are involved, both the Freemancode and the subpixel information can be processed, whereby, if and asrequired, absolute coordinates at subpixel resolution can be generatedfrom the Freeman code and the subpixel information. It is also possibleto represent the subpixel information as separate vectors in the x and ydirections.

[0019] Additional distinguishing characteristics, advantages andfeatures of the invention may be derived not only from the claims whichlist these features—individually and/or in combination—but also from thepreferred designs that may be derived from the following description ofthe drawings. They show:

[0020]FIG. 1 a purely schematic representation of a coordinate measuringdevice for the measurement of an object geometry, with an imageprocessing unit and a display unit.

[0021]FIG. 2: a flowchart of a process for the measurement of an objectgeometry according to the invention.

[0022]FIG. 3: the representation of an object geometry as image contentby means of the display unit, whereby geometric structures suitable forthe measurement of the object are marked and/or selected.

[0023]FIG. 4: the image content of an object geometry, whereby an imageprocessing window is automatically adjusted, in an optimized manner, toa detected geometric structure.

[0024]FIG. 5: the image content of an object geometry, whereby an imageprocessing window is automatically adjusted, in an optimized manner, toa detected geometric structure with reference to direction and position.

[0025]FIG. 6: the image content of an object geometry, whereby an imageprocessing window is automatically adjusted, in an optimized manner, toa detected geometric structure with reference to a part tolerance.

[0026]FIG. 7: a representation of the image content of an object to bemeasured with a regular object structure, whereby the structure locatedclosest to the middle of an image section is automatically selected.

[0027]FIG. 8a-c: various strategies for the extraction of geometricstructures from a predetermined image content.

[0028]FIG. 9: a decision tree for the selection of a measuring processas a function of a predetermined measuring task.

[0029]FIG. 10: a decision tree for the selection of a contour andfeature extraction as a function of workpiece classes.

[0030]FIG. 11a-c: the representation of an object contour in a pixelarray according to Freeman code with supplementary subpixel information.

[0031]FIG. 1 shows, on a purely schematic basis, the structure of acoordinate measuring device 10 for the measurement of an object geometryof an object 12, such as, for example, a workpiece geometry or a toolgeometry, by means of an optical sensor 14, which, in the describedexample, is in the form of an image processing sensor such as a camera,and makes available an image content, for example, in grayscale values.The optical sensor 14 can be moved in the x, y and z directions by meansof the positioning system 16 that is controlled by an axis control 18.The object 12 is placed in an object holder 20 and can, for example, berotatably placed.

[0032] For control of the optical sensor 14, a control unit 22 isprovided, by means whereof, for example, modification of the opticalmagnification can be performed. In addition, a control device 24 isprovided for modification of a light intensity, to which the object 12is exposed at the time of measurement. In addition, a control unit 26,in itself known from prior art, is provided for the control andmonitoring of the additional functions of the coordinate measuringdevice 10.

[0033] For the processing of the image recorded by the optical sensor14, an image processing unit 28 is connected to the coordinate measuringdevice 10, and a display unit 30 is connected to set image processingunit 28, for the representation of an image content 32 corresponding tothe object geometry. The image processing unit 28 includes at least onecomparator 34, an image memory 36, a storage unit 38 for predeterminedregular geometries, and a storage unit 40 for predetermined nominaldata.

[0034]FIG. 2 shows the flow of the process according to the invention.According to a first step 42 of the process, the optical sensor 14 ismoved by means of the positioning system 16 into a position formeasurement of the object 12. The lighting of the object, as well as thenecessary magnification and additional necessary settings, are setautomatically, or manually by an operator, by means of control units 22and 24.

[0035] In a further step 44 of the process, the image content recordedby the optical sensor 14 is read into an image memory 36 and stored. Ina next step 46 of the process, a check is immediately performed in orderto determine whether the image content of the optical sensor 14 has beenmodified. If a modification of the image content is recognized, theimage content is automatically searched, in a step 48 of the process,for geometric structures suitable for the measurement of the object. Ina step 50 of the process, the suitable structures are immediatelymarked—that is, for example, emphasized by means of colored lines,circles or similar structures, or, for example, marked by means of anadjusted window. In a step 52 of the process, the accordinglymarked/selected geometric structures are made available for furtherevaluation—that is, for example, stored.

[0036] The recording of the modification of the image content accordingto step 46 of the process can be implemented in various ways. In apreferred design, the modification of the image content is inferred froma modification of the optical magnification and/or of the position of amechanical axis of the positioning system 16 and/or a modification ofthe light intensity. It is thereby provided that the control unit 22,for the purpose of control of the zoom lens of the optical sensor 14,transmits a signal, for example, by means of a bus 54, to the imageprocessing unit 28, so that, accordingly, a new image content can beread in and, according to step 48 of the process, can then immediatelyand automatically be searched for geometric structures. In addition, itis provided that, for example, by means of a replacement unit 56, suchas a revolving holder, a signal is transmitted to the image processingunit 28 at the time of modification of the optical magnification bymeans of a change of objective. It is also provided that the axiscontrol 18 supplies a signal for the detection of modification of theimage content when the state of a counter on the axes remains constant,following a position change, for longer than a predetermined interval of“dead time”. Furthermore, it is provided that the lighting control 24supplies a signal when a nominal lighting value remains within atolerance range for longer than a predetermined interval of “dead time”.To this end, an additional sensor 58 may be provided, which supplies asignal when the constancy of the light ratios gives rise to an inferencewith regard to the modification of the image content.

[0037] Irrespective of that stated above, it is also possible for themodification of the image content to alternatively be manuallydetermined, for example, by an operator pushing a button, especiallywhen the operator desires to update the represented image content,without performing the aforementioned modifications. With regard to step48 of the process, it should be noted that, for the purpose ofmarking/identification of the geometric structures relevant tomeasurement, a comparison of the contours/geometric elements withregular geometric elements stored in the storage unit 38, such ascircles and straight lines, takes place, whereby the least deviation inshape is used as a criterion. In other words, the image elements, whichare recorded and preferably represented in grayscale values intotwo-dimensional matrix, are matched with predefined regular geometricelements, and if a match or near-match is found, the selected geometricstructure is marked as a function of the criterion of least deviation inshape.

[0038]FIG. 3, purely by way of example, represents the object geometry32 of the object 12 as shown on the display unit 30. The automaticallyselected geometric structures—in the design represented here, straightlines and circles—are represented by dashed markings 60, 62, 64, 66, 68,70, which may also, for example, be emphasized in a different color fromthat of the contour of the object. In the described design, the imagecontent 32 is automatically searched for predefined regular geometricelements, i.e. straight lines and circles, which are then automaticallymarked. The geometric structures thus marked can then be immediatelyevaluated—such as, for example, determination of a radius R of thecircles 68, 70, determination of an angle α between the lines 60, 66, ordetermination of a distance D between the lines 60, 62.

[0039] Alternatively, it is also possible for the automatically proposedgeometric structures and/or contours and elements to be manuallyselected by an operator. It is thereby provided that the markedgeometric structures are selected, for example, by means of a monitorcontrolled by a mouse. In this way, the measurement of the objectgeometries can be limited to desired areas. Moreover, it is possible forthe automatically preselected elements and/or contours to beautomatically incorporated into a characteristic list at the time of anew modification of the image content—for example, by the movement ofthe positioning unit 16, by modification of the lighting or the zoomsetting—so that they can be stored and retrieved for furthermeasurement. In addition, the automatically preselected elements can bemodified and deleted by the operator, or an area of interest from thecontour can be defined by the operator him/herself.

[0040] With regard to feature 50 of the process—that is, themarking/display of the selected geometric structures—it should be notedthat the marking/selection can be performed in a variety of ways. As analternative to the aforementioned marking by means of lines or circles,it is possible, according to a proposal of an inventive nature, for animage processing window (area of interest) to be automatically adjusted,in an optimized manner, to the selected geometric structure and/orgeometric element/contour. Examples are set forth in FIGS. 4 to 6.

[0041] If, for example, the contour of circle 68 is representedaccording to FIG. 4 in a first image content, an image processing window72 is automatically adjusted, in an optimized manner, to the detectedcircle contour, whereby a very precise evaluation can take place. Shouldthe image content be modified, for example, by moving the optical sensor14, a new automatic and optimized adjustment to the currently selectedgeometric element/contour—which, according to FIG. 5, is detected as astraight line—takes place. Image processing windows 74, 76 are adjusted,according to direction and proportion, to the selected lines 64, 66.

[0042] It is also possible for an image processing window 78, by meansof a predefined part tolerance Δ, to be automatically adjusted, in anoptimized manner, to the detected geometric element, such as circle 68,as shown in FIG. 6. Thereby, the circle, with a diameter [Translator'snote: as written in the original German document; this is probably anerror for “a radius”] of R, by way of example, lies within a tolerancerange between R−Δ and R+Δ, so that the image processing window 78 isadjusted to the larger radius R+Δ. This is especially advantageous inthe course of a measurement program for a series of identical objects,as, in this way, intervention by an operator can be systematicallyexcluded.

[0043]FIG. 7 shows the image content 80 of an object geometry withregular geometric structures 82—such as, for example, a semiconductorchip that shows etched structures on its surface. In order to simplifythe evaluation of the marked geometric structures, it is possible, bymeans of a process feature, to provide that, out of the quantity ofpreselected geometric structures 82, the structure 84 located closest tothe center 86 of a monitor section 88 is automatically selected. Thedescribed measure achieves the advantage of not requiring any additionalselections.

[0044] It is also provided that, in the course of automatic measurementof several objects 12 of the same type, both an image processingalgorithm and the image processing window are allocated to the midpointof the respective geometric elements.

[0045]FIGS. 8 and 9 represent various processes which can be used withthe process according to the invention, as a function of the geometricfeatures to be measured, such as for more dimension. Accordingly, by wayof example, FIG. 8 represents an individual scanning process, by meansof which both shape characteristics and dimensions of a contour 90 canbe determined. By means of this process, contour 90 is recorded in asingle scan. The process represented in FIG. 9 is point-by-pointmeasurement, which is used in a conventional manner for thedetermination of dimensions, such as diameter, distance and angle. It isthereby provided that a contour 92, such as a circular contour of adrill hole, is determined by means of several individual measurements94, 96, 98, 100. To this end, the individual measurement 94-100 areevaluated and entered in a mathematical relationship, in order, forexample, to determine dimensions of an object, such as diameter. Inaddition, FIG. 9 represents a scanning process, by which a contour 102is recorded by means of overlapping individual images 104. This processas well can be used for the determination of both shape and dimensions.As stated above, in searching the image content for geometric structuressuitable for measurement, regular geometries such as circles or lines,which are stored in a storage unit 38, can be used. It is also possible,for the purpose of selecting the contour and/or geometric elements, tomake use of nominal data present in a storage unit 40 for comparison, sothat predetermined structures which have already been searched for canbe simply selected.

[0046] A further improvement of the process for measurement of theobject 12 is achieved in that the strategies for contour and featureextraction—such as, for example, binarization modes 1, 2 or 3 as shownin FIG. 10, are determined as a function of object or workpiece classes;that is, as a function of their material, such as metal, plastic orglass, or of their surface qualities, such as light or dark, and/or as afunction of the mode of operation set for the coordinate measuringdevice, such as, for example, direct light processes or transmittedlight processes.

[0047]FIG. 11 shows an design of the process, according to which acontour 108 of the object, which is represented in a pixel raster 106,is described by means of a Freeman code. FIG. 11b shows a single pixel110 with the coefficients for the Freeman coding. In FIG. 11a,coefficients are entered by way of example. Conventional Freeman coding,however, has the disadvantage that a pixel within a conventional pixelarray 106 generally shows an extension of 5 to 10 μm, and accordingly,when measuring structures <5 μm, a high degree of measurementuncertainty occurs. In this respect, there is also a requirement forobtaining information on the course of the contour within a pixel 108.To this end, it is proposed to provide the image processing contour inthe pixel raster with additional information on the subpixel coordinateswithin the pixel. For this purpose, it is provided that the contours 108are written in Freeman chains, represented in FIG. 11c, and that, toevery byte 112 of the Freeman chain, corresponding subpixel bytes 114are added. In subsequent image processing operations, such as zoom,auto-contrast or image correction filters, both the Freeman code 112 andthe subpixel information 114 can be processed. The absolute coordinatescalculated from the Freeman code and the subpixel information can begenerated in subpixel resolution. It is also possible to represent thesubpixel information as separate vectors in the x and y directions.

1. Process for the measurement of an object geometry (12), especially aworkpiece or tool geometry, by means of a coordinate measuring device(10), whereby the object geometry (12) is recorded by means of anoptical sensor (14), such as a camera, and represented as an imagecontent (32), and whereby, within the image content, geometricstructures (60-70) suitable for the measurement of the object (12), suchas geometric elements or contours, are selected and subsequentlyevaluated, characterized in that at the time of any modification of theimage content (32), said image content is automatically searched for thegeometric structures (60-70) suitable for the measurement of the object(12), and the suitable structures are marked and made available forfurther evaluation.
 2. Process according to claim 1, characterized inthat the modification of the image content (32) takes place whenmodification of the optical magnification and/or of the position ofmechanical axes of the coordinate measuring device (10) and/or of thelight intensity is implemented.
 3. Process according to claim 1 or 2,characterized in that the modification of the image content (32) isrepresented by a signal.
 4. Process according to at least one of theprevious claims, characterized in that the signal representing themodification of the image content (32) is produced by a control unit(22) of a zoom lens of the coordinate measuring device (10) at the timeof modification of the optical magnification.
 5. Process according to atleast one of the previous claims, characterized in that the signalrepresenting the modification of the image content (32) is produced by areplacement unit (56), such as a revolving holder, when the modificationof the optical magnification is produced by replacement of theobjective.
 6. Process according to at least one of the previous claims,characterized in that the signal representing the modification of theimage content (32) is produced by an actuation control (18), such as CNCcontrol, when the state of a counter on at least one axis of thecoordinate measuring device (10) remains constant, following a positionchange, for longer than a predetermined interval of “dead time”. 7.Process according to at least one of the previous claims, characterizedin that the signal representing the modification of the image content(32) is produced by a lighting control (24), when a nominal lightingvalue, following a modification of lighting, remains within a tolerancerange for longer than a predetermined interval of “dead time”. 8.Process according to at least one of the previous claims, characterizedin that the signal representing the modification of the image content(32) is produced by an additional optical sensor, when the constancy ofthe light ratios gives rise to an inference with regard to themodification of the image content.
 9. Process according to at least oneof the previous claims, characterized in that the signal representingthe modification of the image content (32) is manually produced by anoperator, preferably by pressing a button.
 10. Process according to atleast one of the previous claims, characterized in that the imagecontent (32) is automatically searched for at least one regulargeometric element, such as a circle and/or a straight line.
 11. Processaccording to at least one of the previous claims, characterized in thatthe automatically proposed geometric structures such as contours andgeometric elements (60-70) are manually selected by an operator, forexample, through the control of a monitor by means of an input devicesuch as a mouse, touchpad, touch screen and so forth.
 12. Processaccording to at least one of the previous claims, characterized in thatthe automatically selected geometric structures can be automaticallyincorporated into a characteristic list at the time of a newmodification of the image content (32).
 13. Process according to atleast one of the previous claims, characterized in that theautomatically preselected elements (60-70) are manually deleted andmodified by the operator, whereby, especially, an area of interest fromthe represented object geometry—such as a contour—can be defined by theoperator him/herself.
 14. Process for the measurement of an objectgeometry preferably according to claim 1, characterized in that foridentification of the relevant geometric structures (60-70) suitable forthe measurement of the object (12), a comparison of the recordedgeometric structures of the object geometry with at least one regulargeometric element, such as a circle and/or a straight line, isperformed, and characterized in that the geometric structures of theobject geometry which show the least deviation in shape, relative to theregular geometric element, are marked.
 15. Process for the measurementof an object geometry preferably according to claim 1, characterized inthat the marking of the geometric structure suitable for the measurementof the object takes place in a manner whereby an image processing window(72, 74, 76, 78) is automatically adjusted to the marked geometricstructure, such as a geometric element or contour.
 16. Process accordingto claim 15, characterized in that an optimized adjustment takes placeby means of a predetermined part tolerance.
 17. Process according toclaim 15 and/or 16, characterized in that the automatic adjustment isperformed with respect to the direction and proportion of the markedgeometric structure (64, 66).
 18. Process for the measurement of anobject geometry preferably according to claim 1, characterized in thatout of the quantity of preselected geometric structures (60-70, 82, 84),the structure located closest to the middle of a represented imagesection (88) is automatically selected.
 19. Process for the measurementof an object geometry preferably according to claim 1, characterized inthat as a function of an object class to be measured and/or the mode ofoperation of the coordinate measuring device (10), strategies for themarking of the geometric structures (60-70) suitable for the measurementof the object (12) are selected and/or determined.
 20. Process for themeasurement of an object geometry preferably according to claim 1,characterized in that the strategies for the marking of the geometricstructures (60-70) suitable for the measurement of the object (12) aredependent upon the type of object material, such as metal, plastic andthe like.
 21. Process for the measurement of an object geometrypreferably according to claim 1, characterized in that the strategiesfor the marking of the geometric structures (60-70) suitable for themeasurement of the object (12) are dependent upon a property ofreflection of the surface of the object (12), such as, for example,light, dark, or similar.
 22. Process according to at least one of theprevious claims, characterized in that as a strategy for contour andfeature extraction, image filters and/or contour filters, such as, forexample, erosion, dilation, Sobel filters or contrast amplifiers areused.
 23. Process for the measurement of an object geometry preferablyaccording to claim 1, characterized in that in the course of anautomatic sweep of several objects (12) of the same type, both an imageprocessing algorithm and the image processing window (74, 76, 78) areallocated to an average value of the respective geometric structures.24. Process for the measurement of a geometric structure, especiallyaccording to claim 1, characterized in that as a function of thegeometric structures suitable for the measurement of the object, variousprocesses such as scanning or point-by-point measurement are accessedfor the purpose of evaluation of a shape, such as a circle, a straightline or similar, or for the purpose of evaluation of a dimension, suchas diameter, distance, angle or similar.
 25. Process for the measurementof a geometric structure, especially according to claim 1, characterizedin that for the selection of the geometric structures, such as contoursand/or geometric elements, available nominal files are used forcomparison.
 26. Process for the measurement of workpiece geometries bymeans of coordinate measuring devices with image processing sensors,especially according to claim 1, characterized in that image processingcontours (108) are provided, within a pixel raster (106), withadditional information with regard to subpixel coordinates within thepixel.
 27. Process according to claim 26, characterized in that thecontours (108) are described by so-called Freeman Chains and thatcorresponding subpixel bytes (114) are added to each byte of the FreemanChain.
 28. Process according to claim 26 or 27, characterized in that inimage processing operations both the Freeman code and the subpixelinformation are processed.
 29. Process according to at least one of theprevious claims,